Polybrominated biphenyls (PBB) have been reported to produce clinical signs of neurological toxicity in humans and neurobehavioral deficits in rats and mice, both in relatively short exposures. The present work is intended to assess neurobehavioral consequences of chronic (six month) exposure to a commercial mixture of PBB (Firemaster FF-1). Rats receive 0.3, 1.0, or 3.0 mg/kg body weight of FF-1 or corn oil vehicle. Mice receive 1.0, 3.0, or 10.0 mg/kg body weight of FF-1, or vehicle. Both male and female rats and mice are to be tested in a battery designed to screen for neurobehavioral dysfunction. Tests for rats include: body weight, motor activity, sensorimotor reflexes or orientation, visual placement, forelimb grip strength, inclined screen, hind limb strength, startle to air puff, and rectal temperature. Shock escape latancies and acquisition of shock avoidance are tested at the end of one month's dosing and retention tested at 2 and 6 months. Mice receive the same tests except for hind limb strength, inclined screen, startle, and lateral hop. Autonomic/general health observations and food consumption measures are taken on all animals.